Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $212.41   12.198%   $238.3198   $238.32   $238.30   $238.30  
  Purchase #2 $242.59   10.870%   $268.9595   $268.96   $268.95   $269.00  
  Purchase #3 $57.37   6.183%   $60.9172   $60.92   $60.90   $60.90  
  Purchase #4 $71.85   9.600%   $78.7476   $78.75   $78.75   $78.70  
  Purchase #5 $163.77   6.316%   $174.1137   $174.11   $174.10   $174.10  
  Purchase #6 $47.96   9.462%   $52.498   $52.50   $52.50   $52.50  
  Purchase #7 $202.90   8.246%   $219.6311   $219.63   $219.65   $219.60  
  7 purchase totals = $998.85       $1,093.1869   $1,093.19   $1,093.15   $1,093.10